1. Field of the Invention
The present invention relates to a defroster for a refrigeration system.
2. Description of the Related Art
Defrosting systems are known in the art. Water based material such a cool vapor, ice or frost aggregates on refrigeration components of merchandisers such as food and beverage display cases in a supermarket. This is a very well known problem in the art, and even more so today with rising energy costs. For the purposes of this application the term frost will also encompass ice or ice like material, snow or snow like material, or cooled water or water vapor, or any deposit (regardless of amount) of minute ice crystals formed when water vapor condenses at a temperature below or at freezing.
Frost from water vapor typically aggregates on an evaporator coil and forms a coating. This coating is detrimental to overall cooling capacity and efficiency of the refrigeration device and must be removed to ensure proper operation of the refrigerator. In commercial supermarkets, the defrosting devices of a low temperature (10 F.-35 F.) refrigeration system have to be actuated for up to two hours a day to remove the frost and ice by heating them. This causes productivity losses and unnecessarily warms the food therein causing possible shorter shelf life or even in the most extreme instances spoilage. Moreover, this causes a messy working condition as water collects at the floor that is mopped.
One such defrosting device that is well known in the art is a resistance heater. Another major defrosting method is to bring a hot gas ejected by the condenser units of a refrigeration system to the evaporator coil. These methods for defrosting are effective in the art, however, both of them often heat not only the evaporator coil but the food or products in the refrigeration compartment an amount. This slight increase in temperature negatively effects shelf life of the stored products. Additionally, extra piping and plumbing is needed for bringing the ejected hot gas from a condenser to a refrigeration system such as a display case. This increases the installation cost for a supermarket.
Also, the hot gas defrosting systems are often a stand alone unit. The condensers in outdoors are located a distance away from the refrigerator. Such an arrangement is not advantageous. Floor space is lost by having additional piping and extra energy is consumed by pumping the hot gas from a distant condenser. Therefore, there is a need for an integrated defrosting unit.
Another drawback of the defrosting devices of the prior art is that they are actuated to “on” for a fixed amount of time. Since the humidity of a supermarket may vary from time to time the amount of ice or frost formed on an evaporator coil and the formation rate would vary accordingly. To activate the defrost devices during a fixed period of time in a day it is likely that the defrosting does not take place when it is most needed and the defrosting process has to be excessive to avoid insufficient frost and ice removal. Again, arbitrary defrosting leads to a slight increase in temperature, which negatively effects a shelf life of the stored products and in the most extreme cases results in spoilage. Thus, there is a need in the art for an automatic defrosting unit.
Still another drawback of the defrosting devices of the prior art is that they are non-productive and cause energy losses. Often, the defrosting device generates a great amount of heat. This heating effect must be later compensated by the refrigeration device once defrosting concludes. The removal of this heat arising from defrosting exerts extra load to the condenser units, which once again leads to lower energy efficiency. This heating and then cooling causes higher energy costs. Again, this heating may cause further losses by heating the products and thereby lessening the shelf life. Thus, there is a need in the art for a localized defrosting that will not extend excessive heat into any other refrigeration components, let alone any food compartment. A thermoelectric cooling/heating device is based on the Peltier effect, which moves heat from one location to another when a current flows through certain semiconductor materials. The thermoelectric modules are operated using direct current that is optimized to gain the best coefficient of performance (COP). The cooling COP of a thermoelectric device operated at its optimal current is given as equation (1).
                              ϕ          c                =                                            T              c                                      (                                                T                  h                                -                                  T                  c                                            )                                ⁢                                    [                                                                    (                                          1                      +                                              ZT                        M                                                              )                                                        1                    /                    2                                                  -                                                      T                    h                                    ⁢                                      /                                    ⁢                                      T                    c                                                              ]                                      [                                                                    (                                          1                      +                                              ZT                        M                                                              )                                                        1                    /                    2                                                  +                1                            ]                                                          equation        ⁢                                  ⁢        1            where Z is the figure of merit, a material property, TM is the average temperature of a heat sink and a heat source, and Tc and Th are the temperatures of a heat source (cold side) and a heat sink (hot side) respectively. The COP for heating is simply the cooling COP plus one. This is given as
                              ϕ          h                =                  1          +                                                    T                c                                            (                                                      T                    h                                    -                                      T                    c                                                  )                                      ⁢                                          [                                                                            (                                              1                        +                                                  ZT                          M                                                                    )                                                              1                      /                      2                                                        -                                                            T                      h                                        ⁢                                          /                                        ⁢                                          T                      c                                                                      ]                                            [                                                                            (                                              1                        +                                                  ZT                          M                                                                    )                                                              1                      /                      2                                                        +                  1                                ]                                                                        equation        ⁢                                  ⁢        2            which is always greater than 1. The energy balance for a thermoelectric module is given asQh=We+Qc  equation 3where Qh is the heating energy generated, We is the electrical energy input which equals I2R (I-current, R-resistance of a thermoelectric module), and Qc is the cooling absorbed from the immediate environment. The heating COP is related to these energy terms by
                              ϕ          h                =                              Q            h                                W            e                                              equation        ⁢                                  ⁢        4            Therefore, to yield a same amount of localized heating Qh a thermoelectric device would consume (1−1/φh)Qh less electrical energy than a conventional resistive heater. Furthermore, a net global heating effect made by a thermoelectric device is also (1−1/φh)Qh less than that an amount generated by a prior resistive heater which is about equal to Qh. Thermo-electric heating benefits the minimization of excessive heating.
Accordingly, there is a need for a cooling system and defrosting system for a refrigeration unit that does not overly heat the refrigeration compartment. There is also a need for a defrosting system that is a compact unit that may be easily manufactured and easily installed in an existing or new system. There is still another need for a defroster that automatically senses the presence of frost, water vapor, ice, snow and automatically defrosts or otherwise removes the material for an optimal operation and an automatic modulation. There is a further need for a defroster that also provides cooling to assist the refrigeration device.
There is also a need for such a defroster that eliminates one or more of the aforementioned drawbacks and deficiencies of the prior art.